NOTE: All distances are approximate. The space telescopes are not shown at their actual altitudes above the atmosphere. Altitude scale is logarithmic.

Certain wavelengths of light — in fact, most of them — never reach the ground. They are absorbed by our atmosphere. Space telescopes placed above our atmosphere can observe these wavelengths.

Most visible and radio wavelengths do reach the ground (see "optical window" and "radio window") and can be observed by ground-based telescopes. A limited amount of infrared (IR) and ultraviolet (UV) light also reaches the ground.